Weather, Climate and Change
Weather & Meteorology Fundamentals
Course 1 · Chapter 8 · Weather, Climate and Change
The first chapter of this course drew a line between weather, what the atmosphere is doing now, and climate, the pattern of weather over decades. This final chapter returns to that line and uses everything since: the layers, the heat and moisture, the winds, the fronts and storms, and the limits of forecasting. The aim is not to settle arguments but to give you the tools to read claims about the climate with a clear head. Dates and figures are given from general knowledge and flagged where they should be checked.
Weather Versus Climate, Again
Climate is usually defined as the average and the variability of weather over a period of thirty years or more (check the standard period used by the World Meteorological Organization). A cold week says very little about the climate, in the same way that one hand of cards says little about the deck. A useful saying is that climate is what you expect and weather is what you get.
The Energy Balance
Everything in this course runs on energy from the sun (see Weather & Meteorology Fundamentals 3). Over time, the Earth must send back out as much energy as it takes in, or it warms or cools. Incoming sunlight is largely shortwave radiation; the Earth emits longwave, infrared radiation. Some gases in the atmosphere, notably water vapour, carbon dioxide and methane, absorb infrared and re-emit it in all directions, including back down. This is the greenhouse effect, and it is not a controversial idea in itself: without it, the average surface temperature would be well below freezing (check the figures, usually quoted at around 33 degrees Celsius difference).
- Natural greenhouse effect: keeps the planet habitable.
- Enhanced greenhouse effect: extra greenhouse gases from human activity, mainly burning fossil fuels and clearing forests, trap more heat. The idea that more carbon dioxide would warm the planet was set out in the nineteenth century, associated with scientists such as Svante Arrhenius (check the names and dates).
- Feedbacks: a warmer atmosphere holds more water vapour, which amplifies the warming; melting ice exposes darker surfaces that absorb more sunlight. Clouds are harder, since they can cool or warm depending on type and height (check).
What the Records Show
Climate scientists build the record from thermometers on land and sea, balloons and satellites, and for the more distant past from indirect evidence called proxies, such as tree rings, ice cores, corals and sediments. Several independent groups produce global temperature series and find broadly the same result: the global average has risen since the late nineteenth century, by a little over one degree Celsius, and the last decade is the warmest in the instrumental record (check the figures against a current source from the World Meteorological Organization, NASA, NOAA, the Met Office or Copernicus).
| Indicator | What is observed | Where to check |
|---|---|---|
| Global temperature | Rising since the late nineteenth century | National and international temperature series |
| Sea level | Rising, from warming water and melting land ice | Tide gauges and satellite altimetry |
| Ice | Arctic sea ice and most glaciers shrinking | Satellite records, glacier surveys |
| Carbon dioxide | Concentration well above the range of the past several hundred thousand years | Direct measurement at Mauna Loa from 1958, and ice cores (check) |
| Extremes | More frequent heat extremes; changes in heavy rain in many regions | National services, the IPCC reports (check) |
The British Isles in a Changing Climate
For a reader in Scotland, the practical questions are local: warmer and wetter winters, heavier downpours, rising sea level on the coast, and changes in the frequency of the extremes covered in Weather & Meteorology Fundamentals 6 (check the projections from the UK Climate Projections and the Met Office). Attributing any single storm to climate change is harder than attributing a trend, which is why scientists speak of changed odds and not of causes of one event.
How to Read a Claim
- Weather or climate? A single cold snap or hot day is weather; a trend over decades is climate.
- Global or local? A cold winter in one region can sit alongside a warm year for the planet.
- Which period and baseline? A graph that starts at a peak or a trough can say almost anything. Ask what period it covers and what it is compared with.
- What is the source? Prefer national weather services, the IPCC assessments and published studies over social media posts and unsourced charts (check the current reports).
- Is the uncertainty stated? A good claim says how sure it is. Be wary of both certainty about everything and doubt about everything.
- Does it fit the physics? Everything here rests on the same ideas as the rest of the course: energy in and out, water, air in motion.
Exercises
A friend says that a cold week in January proves the climate is not warming. Write a short reply using the difference between weather and climate.
Explain the greenhouse effect in a few sentences, and say why it is both natural and capable of being enhanced.
You are shown a chart that appears to prove that temperatures are falling. List four questions you would ask about it before believing it.
Quick Reference
- Climate: the average and variability of weather over thirty years or more
- Greenhouse effect: gases absorb infrared and re-emit it; natural and capable of enhancement
- Records: thermometers, balloons, satellites, and proxies for the distant past
- Natural variability: orbit, sun, volcanoes, ocean cycles; attribution separates it from human influence
- Reading a claim: weather or climate, global or local, which period, what source, what uncertainty